Implications of coral reef buildup for the controls on atmospheric CO2 since the Last Glacial Maximum

We examine the effect on atmospheric CO2 of the occurrence of increased shallow water carbonate deposition and regrowth of the terrestrial biosphere following the last glacial. We find that contrary to recent speculations that changes in terrestrial carbon storage were primarily responsible for the observed similar to20 ppmv late Holocene CO2 rise, a more likely explanation is coral reef buildup and other forms of shallow water carbonate deposition during this time. The importance of a responsive terrestrial carbon reservoir may instead be as a negative feedback restricting the rate of CO2 rise possible in the early stages of the deglacial transition. This separation in time of the primary impacts of regrowth of the terrestrial biosphere and increased shallow water carbonate deposition explains the occurrence of an early Holocene carbonate preservation event observed in deep-sea sediments. We demonstrate that their combined influence is also consistent with available proxy estimates of deep ocean carbonate ion concentration changes over the last 21 kyr. Accounting for the processes that act on the carbonate chemistry of the ocean as a whole then allows us to place strong constraints on the nature of the remaining processes that must be operating at the deglacial transition. By subtracting the net CO2 effect of coral reef buildup and terrestrial biosphere regrowth from recent high-resolution ice core data, we highlight two periods, from 17.0 to 13.8 kyr and 12.3 to 11.2 kyr BP characterized by sustained rapid rates of CO2 increase (> 12 ppmv kyr(-1)). Because these periods are coincident with Southern Hemisphere "deglaciation,'' we argue that changes in the biogeochemical properties of the Southern Ocean surface are the most likely cause

Surface water temperature, salinity, and density changes in the northeast Atlantic during the last 45,000 years: Heinrich events, deep water formation, and climatic rebounds

We developed a new method to calculate sea surface salinities (SSS) and densities (SSD) from planktonic foraminiferal delta(18)O and sea surface temperatures (SST) as determined from planktonic foraminiferal species abundances. SST, SSS, and SSD records were calculated for the last 45,000 years for Biogeochemical Oceanic Flux Study (BOFS) cores 5K and 8K recovered from the northeast Atlantic. The strongest feature is the dramatic drop in all three parameters during the Heinrich ''ice-rafting'' events. We modelled the possibility of deepwater formation in the northeast Atlantic from the SSD records, by assuming that the surface waters at our sites cooled as they flowed further north. Comparison with modelled North Atlantic deepwater densities indicates that there could have been periods of deepwater formation between 45,000 and 30,000 C-14 years B.P. (interrupted by iceberg meltwater input of Heinrich event 3 and 4, at 27,000 and 38,000 C-14 years B.P.) and during the Holocene. No amount of cooling in the northeast Atlantic between 30,000 and 13,000 years could cause deep water to form, because of the low salinities resulting from the high meltwater inputs from icebergs. Our records indicate that after each Heinrich event there were periods of climatic rebound, with milder conditions persisting for up to 2000 years, as indicated by the presence of warmer and more saline water masses. After these warm periods conditions returned to average glacial levels. These short term cold and warm episodes in the northeast Atlantic ate superimposed on the general trend towards colder conditions of the Last Glacial Maximum (LGM). Heinrich event 1 appears to be unique as it occurs as insolation rose and was coeval with the initial melting of the Fennoscandian ice sheet. We propose that meltwater input of Heinrich event 1 significantly reduced North Atlantic Deep Water formation reducing the heat exchange between the low and high latitudes, thus delaying deglaciation by about 1500 radiocarbon years (2000 calendar years)

Climate change: essential knowledge for developing holistic solutions to our climate crisis

Understanding anthropogenic climate change is essential for anyone working in the life sciences. Firstly because climate change has already started to impact the Earth biosphere and human health and these changes need to be documented and acknowledged. Secondly, many of the solutions to climate change, both mitigation and adaptation, will be through the life sciences, everything from massive reforestation and sustainable agriculture to preventing the spread of disease and protecting individual human health. Anthropogenic climate change is, therefore, one of the defining challenges of the 21st century, along with poverty alleviation, environmental degradation and global security. Climate change is no longer just a scientific concern but encompasses economics, sociology, geopolitics, national and local politics, law and health to name a few. Hence, to understand climate change fully then not only does one have to review the science but also the politics and geopolitics, which have created the issue and can provide the solutions. Climate change ultimately makes us examine the whole basis of modern society and ultimately asks questions about humanity's relationship with the rest of the planet

Improving the reproducibility of stable isotope records from planktonic and benthic foraminifera

Foraminiferal oxygen and carbon stable isotope measurements have become an indispensable part of palaeoceanography. It is therefore important to understand and to improve the reproducibility of these measurements. We have estimated the reproducibility of oxygen and carbon stable isotopes of the planktic foraminifera, Globigerina bulloides and Neogloboquadrina pachyderma (sinistral) and the benthic foraminifera Uvigerina peregrina. To obtain stable isotope results from planktic foraminifera with a reproducibility of better than ±0.2%0 we suggest that: (1) tests should be picked from discrete size fractions of less than ±25μrn standardised for each species and ocean, and (2) that at least 30 tests are measured per sample. Isotope measurement of individual tests of the benthic foraminifera U. peregrina heavier than 25 μg give good reproducibility. Below 25 μg both standards and measurements of individual tests show a deviation of up to 0.7%0 from the the 95% confidence limits of larger samples. This we believe is due to a memory effect in the mass spectrometer source. This effect can be reduced by allowing a longer pumping out time of at least 100 seconds between the standard and sample gas measurements. This, however, increases measurement time to 20 minutes per sample, and it can not guarantee reproducible ol3C as there are vital effects associated with growth below 25 μg

Mulga, a major tropical dry open forest of Australia: Recent insights to carbon and water fluxes

© 2016 IOP Publishing Ltd. Mulga, comprised of a complex of closely related Acacia spp., grades from a low open forest to tall shrublands in tropical and sub-tropical arid and semi-arid regions of Australia and experiences warm-to-hot annual temperatures and a pronounced dry season. This short synthesis of current knowledge briefly outlines the causes of the extreme variability in rainfall characteristic of much of central Australia, and then discusses the patterns and drivers of variability in carbon and water fluxes of a central Australian low open Mulga forest. Variation in phenology and the impact of differences in the amount and timing of precipitation on vegetation function are then discussed. We use field observations, with particular emphasis on eddy covariance data, coupled with modelling and remote sensing products to interpret inter-seasonal and inter-annual patterns in the behaviour of this ecosystem. We show that Mulga can vary between periods of near carbon neutrality to periods of being a significant sink or source for carbon, depending on both the amount and timing of rainfall. Further, we demonstrate that Mulga contributed significantly to the 2011 global land sink anomaly, a result ascribed to the exceptional rainfall of 2010/2011. Finally, we compare and contrast the hydraulic traits of three tree species growing close to the Mulga and show how each species uses different combinations of trait strategies (for example, sapwood density, xylem vessel implosion resistance, phenological guild, access to groundwater and Huber value) to co-exist in this semi-arid environment. Understanding the inter-annual variability in functional behaviour of this important arid-zone biome and mechanisms underlying species co-existence will increase our ability to predict trajectories of carbon and water balances for future changing climates

The role of orbital forcing in the Early Middle Pleistocene Transition

The Early Middle Pleistocene Transition (EMPT) is the term used to describe the prolongation and intensification of glacial-interglacial climate cycles that initiated after 900,000 years ago. During the transition glacial-interglacial cycles shift from lasting 41,000 years to an average of 100,000 years. The structure of these glacial-interglacial cycles shifts from smooth to more abrupt 'saw-toothed' like transitions. Despite eccentricity having by far the weakest influence on insolation received at the Earth's surface of any of the orbital parameters; it is often assumed to be the primary driver of the post-EMPT 100,000 years climate cycles because of the similarity in duration. The traditional solution to this is to call for a highly nonlinear response by the global climate system to eccentricity. This 'eccentricity myth' is due to an artefact of spectral analysis which means that the last 8 glacial-interglacial average out at about 100,000 years in length despite ranging from 80,000 to 120,000 years. With the realisation that eccentricity is not the major driving force a debate has emerged as to whether precession or obliquity controlled the timing of the most recent glacial-interglacial cycles. Some argue that post-EMPT deglaciations occurred every four or five precessional cycle while others argue it is every second or third obliquity cycle. We review these current theories and suggest that though phase-locking between orbital forcing and global ice volume may occur the chaotic nature of the climate system response means the relationship is not consistent through the last 900,000 years

A synthesis of the theories and concepts of early human evolution

Current evidence suggests that many of the major events in hominin evolution occurred in East Africa. Hence, over the past two decades, there has been intensive work undertaken to understand African palaeoclimate and tectonics in order to put together a coherent picture of how the environment of Africa has varied over the past 10 Myr. A new consensus is emerging that suggests the unusual geology and climate of East Africa created a complex, environmentally very variable setting. This new understanding of East African climate has led to the pulsed climate variability hypothesis that suggests the long-term drying trend in East Africa was punctuated by episodes of short alternating periods of extreme humidity and aridity which may have driven hominin speciation, encephalization and dispersals out of Africa. This hypothesis is unique as it provides a conceptual framework within which other evolutionary theories can be examined: first, at macro-scale comparing phylogenetic gradualism and punctuated equilibrium; second, at a more focused level of human evolution comparing allopatric speciation, aridity hypothesis, turnover pulse hypothesis, variability selection hypothesis, Red Queen hypothesis and sympatric speciation based on sexual selection. It is proposed that each one of these mechanisms may have been acting on hominins during these short periods of climate variability, which then produce a range of different traits that led to the emergence of new species. In the case of Homo erectus (sensu lato), it is not just brain size that changes but life history (shortened inter-birth intervals, delayed development), body size and dimorphism, shoulder morphology to allow thrown projectiles, adaptation to long-distance running, ecological flexibility and social behaviour. The future of evolutionary research should be to create evidence-based meta-narratives, which encompass multiple mechanisms that select for different traits leading ultimately to speciation

Magnetic susceptibility variations in Upper Pleistocene deep-sea sediments of the NE Atlantic: Implications for ice rafting and paleocirculation at the Last Glacial Maximum

Magnetic susceptibility (MS) variations are used to intercorrelate 17 Upper Pleistocene sediment cores taken from the NE Atlantic, between 40 degrees and 60 degrees N. The MS-based correlation depends on regionally consistent patterns of variation in the deposition of ice-rafted detritus (IRD) in response to Pleistocene glaciations, and especially to high-frequency ice-rafting episodes referred to in recent studies as ''Heinrich events.'' The sedimentological and rock-magnetic basis for the apparent relationship between the MS signal and IRD content of NE Atlantic sediments is examined by (1) comparing the MS profiles of selected cores with their records of coarse fraction (>150 mu m) lithic fragment abundance and Neogloboquadrina pachyderma (sin) percentages, and (2) normalizing MS by expressing it both on a carbonate-free basis, and as a quotient with anhysteretic remanent magnetization (a parameter sensitive to magnetic mineral grain size variations). These comparisons show that variations in bulk-sediment MS are only partly driven by simple carbonate dilution (+/- productivity and dissolution) effects. Changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk MS values. In particular, horizons rich in IRD are associated with significant increases in the relative proportion of coarse grained (multidomain) ferrimagnetic particles in the sediment. This is because ice-rafting, in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments, has a high potential for delivering large ferrimagnetic grains as components of sand-sized, polycrystalline lithic fragments. This fundamental linkage between the IRD content and MS signal of NE Atlantic sediments is used to reconstruct the patterns of variation in IRD deposition and, by inference, surface currents of the last glacial maximum (LGM, similar to 18-19 ka) relative to the present-day NE Atlantic, using the time-slice mapping approach developed by the CLIMAP project group. Our LGM/Holocene MS ratio map, based on sample pairs from over 80 deep-sea cores, confirms that there was a weak, cyclonic gyre north of the polar front in the LGM North Atlantic. The gyre comprised a sluggish warm current in the NE Atlantic flowing north between latitudes 47 degrees and 62 degrees N, partly fed by subtropical waters from south of the polar front, and carrying large numbers of icebergs derived from several sources, most of which melted between Latitudes 45 degrees and 52 degrees N. The warm current probably continued its flow into the Iceland Basin, where it fed into a south-flowing current which transported melting icebergs from Iceland and Scandinavia along the western flank of the Reykjanes Ridge